I found these cards not too long ago, they likely belonged to my late grandmother but I'm puzzled, it's the first time I ever see this type of deck. They're made of plastic, the printings are very classical but aren't of great quality, and the cards are about 5mm less wide than your usual Bicycle card. Does anyone knows what deck this is?

Beautiful backs on those.Most of my "made in china" decks have copy-cat bee backs, or something more geometric. None of them are plastic. They can have very odd/interesting aces and jokers.

Jase has probably given you the most information you can have on these. So many decks have come from Hong Kong, with such a huge variety of "brands" on the boxes, that you may never find exactly what these particular decks were called.